Fixes restoring on AMBA serial line. That is /dev/ttyAMA0,
which is the default serial port to use on qemu-system-aarch64.
(at least in those articles, which I meet it's in boot cmdline)
Also should add support for C/R /dev/ttyUSB*

One may check major numbers on
https://www.kernel.org/doc/Documentation/devices.txt
Also by grepping on kernel repository.

Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>